A kind of grinding semiconductor wafer power on-line measurement device and control method for grinding
Technical field
The invention belongs to hard crisp semiconductor wafer Ultraprecision Machining field, relate to a kind of real-time measurement three-dimensional grinding force and the grinding semiconductor wafer device for measuring force and the control method for grinding thereof of its value as control emery wheel feeding.
Background technology
Semiconductor wafer is to make important backing material in the integrated circuit (IC) at present, and in IC chip processing procedure, the leveling processing that the superfine grinding technology is mainly used in the wafer preparation is processed with the chip back surface attenuate in road, the back processing procedure.Along with IC chip constantly develops to highly integrated, densification and high performance direction, the semiconductor wafer diameter constantly increases, the ever-increasing while of original thickness, the final thickness of required wafer but constantly reduces, therefore the removal amount of material increases on the one hand, for saving the time of follow-up polishing processing, need to increase the grinding removal amount, improve grinding efficient; Under the situation that the intensity of thin wafer reduces greatly, avoiding fragment greatly, need reduce the damage to wafers layer on the other hand, thereby obtain the low undamaged surface of ultra-smooth.Above-mentioned processing request proposes new challenge for the superfine grinding of semiconductor wafer.
The semiconductor wafer grinding machine is mainly used in the laminar semiconductor wafer of grinding, and in the superfine grinding wafer process, grinding force is the major parameter of processing, is an important indicator estimating grinding wafer performance quality.Grinding force is except with grinding dosage is relevant, also (method of traditional monitoring emery wheel situation has modes such as acoustic emission, sound and vibration with the material of emery wheel itself and characteristic, but there is certain limitation in these methods), workpiece to be machined material, surface roughness, grinding ratio, factors such as grinding fluid are relevant.When the grinding wafer, if adopt the constant mode of grinding dosage (stock removal and feed speed) of present wafer grinding machine, the grinding force of generation is also with difference.Like this, grinding force always is among the variation in grinding process, if grinding force is too small, though the wafer quality of processing can be relatively good, reduces production efficiency, makes grinding machine be not fully utilized in process of production; Otherwise, if the grinding force in the grinding process is excessive, will produce harmful effect for the grinding wafer quality that belongs to hard brittle material, increase as surface roughness, cause the damage on the surface and the inferior surface of grinding wafer, wafer surface can be burnt, the wearing and tearing aggravation of emery wheel, and emery wheel bursts apart, even wafer is chipping, especially in the grinding of chip back surface attenuate, during wafer thickness less (≤150 μ m), it all will be fatal destruction that small grinding force impacts.More than these all are the problems that often occurs in the real process of grinding, so this control mode of constant grinding consumption is difficult to guarantee simultaneously grinding accuracy, efficient and the yield rate of semiconductor wafer surface.How solving the contradiction between high-precision grinding and the high-efficiency grinding, is urgent problem.
At present, wafer grinding machine on the production line, as the wafer grinding machine of the Japanese DISOC DFG8000 of company series and the wafer grinding machine of the Japanese Okamoto GNX of company series, adopt the method for the electric current of monitoring driving emery wheel electricity consumption main shaft to reflect grinding force indirectly more, judge with this whether electric main shaft transships.Though this method is simple, when the thicker wafer of grinding, wafer is also insensitive to grinding force, also can satisfy the grinding requirement; But when the grinding LED reverse mounting type, the intensity of wafer significantly reduces, and grinding force also enlarges markedly the influence of wafer thereupon, is difficult in and obtains desirable surface accuracy and yield rate when guaranteeing grinding efficiency.This current value is difficult to reflect grinding force accurately and real-time in addition, can't be with the input signal of current value as the control grinding.In the research wafer grinding machine of people such as Jeremiah A research and development capacitance sensor is installed on air spindle stator and rotor, the mode indirect monitoring grinding force of measuring relative displacement between stator and the rotor changes, but this method is only applicable to measure small grinding force situation.People such as Hyunjin Kim use the three-dimensional dynamometer 9257B of Kistler company to measure the grinding force of silicon chip, and realize constant force griding, but this dynamometer is an absolute construction, and are not fully-integrated with grinding machine, are not suitable for industrialization wafer grinding machine equally.The U.S. 7AF/7AG of Strasbaugh company wafer grinding machine is equipped with the axial force measuring system, and pressure sensor is installed on the emery wheel tooth, can carry out the grinding of grinding force self adaptation, and its institute's grinding force of surveying only is axial force, the grinding force of other both directions is not measured.
The grinding force that produces in the grinding wafer process is decomposed into the power of three directions: axial force F z, influences grinding skin precision and surface roughness; Tangential force Ft, the power that is consumed when influencing grinding, reflection wheel grinding state; Radial load Fr influences residual stress behind the grinding wafer.Three direction power are variant to the influence of grinding efficiency and grinding quality, have only comprehensive monitoring could reflect the grinding situation better, for the grinding parameter of optimizing semiconductor wafer provides foundation.Can real-time online measuring three-dimensional grinding force, and realize that efficient high-quality ultraprecise based on the control grinding force is processed into and be badly in need of the technical problem that solves.
Summary of the invention
The present invention is directed to there is the contradiction between working (machining) efficiency and surface quality in semiconductor wafer and how obtains the high accuracy wafer surface in the superfine grinding process problem, in conjunction with the design feature of the wafer grinding machine of researching and developing and the distribution situation of grinding medium plain emery wheel and the mutual active force of wafer, proposition utilizes a kind of piezoelectric type grinding force on-line measurement device to come dynamic real-time monitoring three-dimensional grinding force, and method of grinding wafer and implement device by the measurement feedback control feed speed and the amount of feeding, to realize high efficient grinding and constant force griding semiconductor wafer.
Technical scheme of the present invention is as follows:
A kind of grinding force on-line measurement device of grinded semiconductor wafer, and as the feedback element of control grinding.This grinding force on-line measurement device adopts the piezoelectric type measuring principle, comprises grinding force measurement mechanism and data processing unit.Sensor unit is a circle ring, comprise 4 groups of piezoelectric quartz force sensors, upper cover plate, lower cover and attachment screws, 4 groups of piezoelectric quartz force sensors are by can measure radial load Fr, tangential force Ft and three direction power of axial force F z three groups quartzy brilliant compositions, one group of X0 ° of cut type of bearing the tension and compression effect wherein, two groups of Y0 ° of cut types of bearing shearing effect, electrode is posted on every group of quartz wafer surface, after quartz wafer is connected in parallel, draws through hollow screw by lead.Piezoelectric quartz force sensor is a hollow structure, on every side with fluid sealant sealing, be evenly distributed on base upper surface etc. on the radius distribution circle, attachment screw is rigidly connected base, upper cover plate and 4 groups of piezoelectric quartz force sensors.This grinding force measurement mechanism is installed between grinding wheel spindle and the spindle drum, that is: the flange upper surface of grinding wheel spindle is connected by screw with grinding force measurement mechanism lower surface, and the lower surface of spindle drum is connected by screw with grinding force checkout gear upper surface.Data processing unit comprises data collecting system, digital control system and servo-drive system, the grinding force value of analyzing and processing grinding force measurement mechanism output.
The method of utilizing described grinding semiconductor wafer power on-line measurement device to carry out the control grinding is:
The static force that in the grinding wafer process, produces, dynamic force and transient force, act on 4 groups of piezoelectric quartz force sensors, piezoelectric quartz force sensor output and grinding force Fx, Fy and Fz are in the same way and the quantity of electric charge corresponding with grinding force, data collecting system receives the charge signal of 4 piezoelectric quartz force sensors and changes, filtering is handled, linear according to grinding force and voltage, calculate grinding force Fx, Fy and Fz, transfer of data after the processing is to digital control system, digital control system compares the user preset parameter in the data that receive, adjust the emery wheel feed speed and the amount of feeding in real time according to comparative result FEEDBACK CONTROL servo-drive system then.
Utilize described grinding semiconductor wafer power on-line measurement device, in process, grinding force is monitored in real time, according to of the reasonable control of grinding force value feedback, to guarantee the safety of crudy and process grinding dosage.The present invention can realize the control grinding, comprises high efficient grinding and constant force griding dual mode.Wherein the method for high efficient grinding is, at corase grind during wafer, is guaranteeing that the grinding under the maximum state of control grinding force improves the grinding speed and the amount of feeding surplus with quick removal wafer as far as possible under the prerequisite of the highest grinding efficiency; The method of constant force griding is, when the correct grinding wafer, need to improve grinding accuracy, the control grinding force guarantees that grinding process carries out under the ductility territory, promptly control grinding force and maintain grinding under grinding under the minimum state or the best grinding process condition, adjust the emery wheel feed speed and the amount of feeding in real time, thereby guarantee the optimal process quality of wafer.In the different grinding stages, need to adopt different grinding dosages, as fast feed grinding when initial, low speed feeding grinding before the end of a period grinding.
The invention has the beneficial effects as follows: detect three direction grinding forces in the grinding wafer process real-time and accurately, and the emery wheel feed speed and the amount of feeding are adjusted in real time according to the grinding force size, realize the monitoring of grinding process, improve the reliability and the production efficiency of process.For improving wafer process precision and surface quality, guarantee that the yield rate of wafer is significant.
Used piezoelectric type grinding force measurement mechanism has rigidity height, good linearity, highly sensitive, sluggish little, intrinsic frequency advantages of higher, is highly suitable for dynamic grinding force measurement.This measurement mechanism is applied to the wafer grinding machine, has compact conformation, dynamometry intermediate link is few, and to the little characteristics of original grinding machine structural modification.Therefore in addition, for the grinding machine of the many main axle structures of multistation, main shaft quantity generally is less than workbench quantity, the grinding force checkout gear is installed on the quantity that structure on the main shaft can reduce the grinding force checkout gear, saves cost.Grinding force on-line measurement link is few, response speed is fast, precision is high; Can improve the grinding efficiency of semiconductor wafer, reduce damage layer thickness.
Description of drawings
Fig. 1 semiconductor wafer grinding machine structural representation.
Fig. 2 grinding force measurement mechanism installation site schematic diagram.
Fig. 3 piezoelectric quartz force sensor signal wiring schematic diagram.
Fig. 4 control grinding system schematic diagram.
The control flow chart of Fig. 5 control grinding system.
Fig. 6 emery wheel feeding curve map.
Among the figure: 1 semiconductor wafer grinding machine; 2 lathe beds; 3 columns; 4 servomotors; 5 screw mechanisms; 6 line slideway mechanisms; 7 slide carriages; 8 grinding wheel spindles; 9 spindle drums; 10 emery wheels; 11 suckers; 12 workbench; 13 attachment screws; 14 attachment screws; 15 grinding force checkout gears; 151 piezoelectric quartz force sensors; 152 attachment screws; 153 upper cover plates; 154 lower covers; Semiconductor wafer W; 16 data collecting systems; 17 digital control systems; 18 servo-drive systems
The specific embodiment
Combination technology scheme and accompanying drawing describe specific embodiments of the invention in detail.
As shown in Figure 1, the structure of semiconductor wafer grinding machine 1 adopts vertical structure, has step-like lathe bed 2, at the upper right side of lathe bed 2, column 3 is being set uprightly.At the medial surface of this column 3, be provided with a pair of straight line guide rail mechanism 6 vertically.Spindle drum 9 fixedly is assemblied on the slide carriage 7.Slide carriage 7 is installed in the line slideway mechanism 6, is connected with screw mechanism 5 simultaneously, and screw mechanism 5 is placed (along Z-direction) along line slideway mechanism 6 directions, is connected with the axle of servomotor 3 on being installed in column 2.Screw mechanism 5 is by the driving of servomotor 3.Emery wheel 10 is installed on the lower end of main shaft 8, and rotates synchronously with main shaft 8.Along with the rotation of servomotor 3, emery wheel 10 vertically moves.
Semiconductor wafer grinding machine 1 also has columned workbench 12.The sucker 11 that is provided on the workbench 12 rotates synchronously with workbench 12.The thin discs shape semiconductor wafer W that grinding is used is adsorbed on the sucker 11 under vacuum action.
As shown in Figure 2, grinding force checkout gear 15 is installed between main shaft 8 and the spindle drum 9, concrete installation method is: 4 groups of piezoelectric quartz force sensors 151 are installed between the groove lower surface of lower cover 154 upper surfaces of main shaft 5 and upper cover plate 153, connect respectively and apply certain pretightning force by 4 groups of attachment screws 152.During installation, earlier lower cover 154 is fixed on the flange upper surface of main shaft 8, with attachment screw 13 upper cover plate 153 is fixed on the lower surface of spindle drum 9 again with attachment screw 14.
As shown in Figure 3, grinding force monitoring device 15 has 4 groups of piezoelectric quartz force sensors 151, is respectively A1, A2, A3 and A4, and every group of piezoelectric quartz force sensor 151 has identical structure.With one group of A1 wherein the structure of piezoelectric quartz force sensor 151 is described, A1 is made of three pairs of quartzy brilliant groups, amounts to 6 bauerite wafers, and this 6 bauerite wafer surface is posted electrode respectively, and piezoelectric quartz force sensor 151 usefulness fluid sealants seal.X0 ° of cut type of tension and compression effect born in wherein a pair of employing, and this takes the electric axis relative direction to place to two bauerite wafers in the quartzy brilliant group, two bauerite wafers post electrode at the interface, be used to export the electric charge of corresponding axial force Fz; Other two pairs are adopted the identical Y0 that bears shearing effect ° cut type, two bauerite wafers in every pair of quartzy brilliant group in the quartzy brilliant group of this two couple take the mechanical axis relative direction to place, the quartzy brilliant group difference of this two couple is: the placement of the light shaft positive cross direction of the quartzy brilliant group of this two couple in horizontal plane, two bauerite wafers in every pair of quartzy brilliant group post electrode at the interface, can export the electric charge of corresponding radial load Fr and tangential force Ft respectively.The electrode at the interface of every pair of quartzy brilliant group output in parallel back ground connection.Then with the output electrode of 4 groups of piezoelectric quartz force sensors 151 (A1, A2, A3 and A4) one by one correspondence be connected in parallel, draw by lead.The calibration result of grinding force monitoring device axial force F z performance is as shown in table 1.
Table 1 grinding force monitoring device axial force F z performance is demarcated
Example: the laboratory room temperature is 26 ℃, and the sensitivity of charge amplifier YE5850B is respectively SX=7.93pc/kgf, SY=7.85pc/kgf, SZ=3.53pc/kgf.Draw by table 1, when loading Fz, nonlinearity erron<0.2%, repeatability error<0.5% is to a laterally interference<2%.Result of the test shows that every index all reaches international production engineering research association-cutting Science and Technology Commission specified standard.
As shown in Figure 4, when the grinded semiconductor wafer W, grinding force passes to main shaft 8 by emery wheel 10, flange through main shaft 8 passes to grinding force checkout gear 15 again, export the charge signal of corresponding radial load Fr, tangential force Ft and axial force F z respectively, be enlarged into corresponding voltage through data collecting system 16 modulation, after the A/D conversion becomes voltage analog signal into data signal Ur, Ut, Uz, as digital control system 17 one of them input signal, draw space vector power numerical value through digital control system 17 respective handling.It is the predefined grinding force numerical value of user that digital control system 17 also receives another, control system compares these two numerical value and calculates the feedback signal of a difference as the grinding force on-line measurement system, export to servo-drive system 18, thereby the rotating speed and the amount of spin of control motor 4, and then reach the feed speed and the amount of feeding of controlling emery wheel 10.Handle in order to follow-up data by terminal demonstration, record, measured radial load Fr, tangential force Ft and the axial force F z of printing at last.
As shown in Figure 5, the grinding force control flow of described grinding force on-line measurement system, the wherein implication of physical quantity representative:
N0: the predefined initial feed speed of user
N δ: the feed speed increment after the calculating
N: current feed speed
F0: the predefined given grinding force value of user
ε: the predefined grinding force rate of change of user
F1: the grinding force value of a last sampling
F2: the grinding force value of current sampling
Illustrate:
Control principle: the grinding force value F1 of the grinding force value F2 of more current sampling earlier and a last sampling, the variation tendency of judgement grinding force.The predefined initial grinding force value F0 of the grinding force value F2 of more current sampling and user is worth comparison most again, judges whether to change current feed speed then.
When the grinding force of being monitored reduces, if current grinding force greater than set grinding force higher limit, keeps current feed speed; If current grinding force is less than set grinding force higher limit, then digital control system 17 is exported to servo-drive system 18 control servomotors 4 with result of calculation, increases current feed speed.When the grinding force of being monitored increased, greater than set grinding force lower limit, then digital control system 17 was exported to servo-drive system 18 control servomotors 4 with result of calculation, reduces current feed speed as if current grinding force; If current grinding force less than set grinding force lower limit, keeps current feed speed.
As shown in Figure 6, for solving the contradiction between high accuracy and the high-efficiency grinding, adopt the emery wheel mode of feeding stage by stage, the grinding stage is divided into soon, F.F., slow-motion, tarry matter, moves back slowly, rewind down, disappears seven stages of crack, adopt different grinding process in the different grinding stages, grinding wafer in the i.e. grinding force after optimization, the feed speed and the range of feeds.In grinding process, monitor the situation of change of grinding force in real time, control the feed speed of grinding wheel spindle by the numerical value change of grinding force by device for measuring force.Test by grinding process parameters early stage in grinding, obtain the grinding force threshold value under the situations such as different chips material, process conditions, technological parameter, again by these grinding test data being set up a comprehensive technological parameter database, this database function does not still provide the grinding force threshold value under the same process parameter, and by analyzing and calculating, can provide the grinding parameter of optimization at special grinding situation, guarantee under different condition, also can obtain processing effect preferably.
As monitoring means in the grinding process and axis feeding control system element, can realize constant force griding and wafer precision grinding machining efficiently by above-mentioned grinding force on-line measurement device.As become soon and fast forward stage carry out constant force griding, guarantee that actual grinding force value is near predefined grinding force allowable value, and maintain in the grinding force scope of setting, thereby guarantee that emery wheel is with maximal rate feeding grinding wafer, remove most of wafer surplus fast, realize the high efficient grinding of semiconductor wafer, constant force griding conditional curve as shown in phantom in Figure 6; The slow-motion stage is then by reducing the mode of emery wheel feed speed, and the grinding of wafer is controlled in the scope of ductility territory, reduces surface and sub-surface damage, obtains the high accuracy wafer surface, solves the high efficiency and the high-precision grinding problem of wafer.